Detector



Sept. 6, 1938. K. S'CHLESINGER DETECTOR Original Filed Nov. 7, 1934 Jake/#0,. M W

Patented Sept. 6, 1938 UNITED STATES PATENT QFFECE DETECTOR Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe,

Steglitz, Germany Berlinber 10, 1933 3 Claims.

In the rectification of carrier waves preferably modulated with a frequency band of large width, e. g., as occurring in television, there are employed with advantage grid detector arrangements, preferably of the push-pull type, as in these rectifiers the carrier wave is removed from the output circuit by compensation, a disturbing grain in the image thus being avoided. In this connection it is necessary, generally speaking, assuming it is desired to avoid an expensive reversing tube, to employ transformers, as already shown by the applicant in his earlier application No. 747,011 and Patent 2,068,769. With transformers of this nature, however, there is encountered the characteristic difliculty that, generally speaking, the secondary potential is in no way symmetrically positive and negative against earth, but always reveals a one-sidedly directed additional potential.

The stated methods are of significance only in connection withfreely oscillating coils, the centres of which cannot be earthed in direct fashion. This connection alrises consequently upon use of the push-pull detector without grid condensers as in the patent application No. 747,011.

The present invention is an improvement of grid-current detector arrangements preferably of those operated in push-pull connection and is a division of Patent 2,072,315. By the arrangement according to the present invention it is possible by special construction of therectifier valve to have in fact a sufficient blocking of the modulation potential against short-circuiting by the high frequency input coil of the detector valve and at the same time good efiiciency. The present invention is relative to a particlular embodiment of a grid current detector arrangement, more particularly for television purposes, wherein a detector valve is employed having control electrodes comprising at least one grid, which is insulated completely or incompletely from the inner electronic discharge space and is furnished with a conductive layer arranged on the insulating coating thereof. In a preferred form of the present invention a double grid detector valve is employed in push-pull fashion in connection with transformer input coupling.

In a preferred form of the present invention set forth in the accompanying drawing there is employed as detector a valve l9 having an insulated grid, or preferably two insulated grids 20, 2|, which are similar and have the same amplification factor and arranged to co-operate with the common cathode 23, and are furnished with a good insulating coating, on the surface of which, however, there is provided a conductive layer 24, which is common to both grids and may be connected with a terminal 22. Valves of this character have for television purposes, in accordance with the invention, the following advantages.

A potential produced in the push-pull. transformer coil 4 may be applied directly and unweakened to the grids 20, 2| without grid condensers, which on account of their requisite small size would mean a considerable loss in sensitiveness. Since these grids are insulated against the interior of the Valve, the middle of the transformer 4 may be connected directly with earth. An incoming particular positive half-wave causes the outer coating 24 common to both grids to be charged negatively. This charge is leaked away by a resistance 25, which may either be provided outside of the valve, or alternatively the leak may be provided inside the valve by making the insulating layer slightly conductive. As will be apparent, it is possible, particularly in. the latter case, to reduce considerably the capacity of the arrangement, and in consequence to employ a comparatively larger grid leak resistance 25 than in the circuits shown in Patent 2,068,768, so that the sensitiveness of the arrangement may be further increased as compared with the previous arrangement with the same lack of inertia. Owing to the possibility of earthing the transformer coil 4 in direct fashion, the danger of lack of symmetry is practically obviated, so that proper compensation of the carrier wave is possible.

I claim:

1. A push-pull grid-current detector arrangement, more particularly for television purposes comprising a detector valve having two separate grids connected in push-pull, anda secondary of an input transformer, said two grids being arranged with the same amplification factor opposite a common cathode which is directly earthed and being insulated from the inner electronic discharge space by an insulating coating and furnished with a conductive coating arranged on the insulating coating, and common to both grids, the ends of said secondary being earthed in its midpoint and connected directly to the grids, said conductive coating being connected to the oathode of said valve.

2. A push-pull grid-current detector arrangement, more particularly for television purposes comprising a detector valve having two separate grids connected in push-pull, and a secondary of an input transformer, said two grids being arranged with the same amplification factor oppoan input transformer, said two grids being arranged With the same amplification factor opposite a common cathode which is directly earthed and being insulated from the inner electronic discharge space by an insulating coating and furnished with a conductive coating arranged on the insulating coating thereof, and common to both grids, the ends of said secondary earthed in its midpoint connected directly to the grids, said conductive coating being directly connected to the cathode of said valve, said insulating coating consisting of a semi-conductive material.

KURT SCHLESINGER. 

